THIOL/ISOCYANATE/(POLY-)ENE FORMULATIONS FOR ADDITIVE MANUFACTURING

Abstract

The present invention refers to a photo-curable composition comprising at least one polythiol having at least two thiol groups, at least one polyisocyanate having at least two isocyanate groups, at least one (poly-)ene compound having at least one —C═C group, and at least one photolatent base catalyst. Furthermore, the present invention pertains to a method of photo-curing the photo-curable composition according to the present invention as well as to a method of three dimensional printing an object with the photo-curable composition according to the present invention. Moreover, the present invention refers to a cross-linked polymer or a three-dimensional object obtained by the methods according to the present invention, and use of the polymer or the object as an antireflective coating, encapsulant for LEDs, microlense for CMOS image sensors, as optical material, as biomedical functional coating, packaging and textile, stents, scaffolds, dental applications, and as reversible adhesive for debond on demand applications.

Claims

1. A photo-curable composition comprising or consisting of A) at least one polythiol having at least two thiol groups; B) at least one polyisocyanate having at least two isocyanate groups; C) at least one (poly-)ene compound having at least one —C═C group; D) at least one photolatent base catalyst; and E) optionally at least one additive.

2. The photo-curable composition according to claim 1, wherein the at least one polythiol i) has two to six thiol groups; ii) is selected from primary and secondary aliphatic and oligomeric thiols having a molecular weight up to 5,000 g/mol; or iii) is selected from di-pentaerythritol tetra(3-mercapto-propionate), pentaerythritol tetra(3-mercaptopropionate), trimethylol-propane tris(3-mercaptopropionate), glycol di(3-mercaptopropionate), pentaerythritol tetramercaptoacetate, trimethylol-propane trimercaptoacetate, glycol dimercaptoacetate, ethoxylated trimethylolpropane tri(3-mercaptopropionate), propylene glycol-2,4,6-triallyloxy-1,3,5-triazine 3-mercaptopropionate, tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, polycaprolactone tetra 3-mercaptopropionate, pentaerythritol tetrakis(3-mercaptobutylate), 1,4-bis(3-mercaptobutylyloxy)butane, 1,3,5-tris(3-mercaptobutyloxethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trimethylolpropane tris(3-mercarptobutyrate) or mixtures thereof.

3. The photo-curable composition according to claim 1, wherein the at least one polyisocyanate i) has two to six isocyanate groups; ii) has a number average molecular weight of 500 to 25,000 g/mol; or iii) is selected from 1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione, (E)-3,5-bis(6-isocyanatohexyl)-6-((6-isocyanatohexyl)imino)-1,3,5-oxadiazinane-2,4-dione or a mixture thereof.

4. The photo-curable composition according to claim 1, wherein the at least one (poly-)ene compound i) has one to six —C═C groups; ii) is a (meth)acrylic compound with a molecular weight of up to 10,000 g/mol; iii) is selected from isobornyl acrylate, 2-phenoxyethyl acrylate, 2,4,6-tribromophenyl acrylate, 1,6-hexanediol diacrylate, 1,10-decanediol diacrylate, 3-methyl-1,5-pentanediol diacrylate, tricyclodecanedimethanol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipropylene glycol diacrylate, ethoxylated bisphenol acrylate A diacrylate, ethoxylated hexanediol diacrylate, polyethylene glycol diacrylate, propoxylated neopentyl glycol diacrylate, urethane-, thiourethane-, epoxy- and polyester-end-capped acrylate oligomers, 2,4,6-tribromophenyl acrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, 2-phenoxyethyl methacrylate, ethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, ethoxylated bisphenol A dimethacrylate, tricyclodecanedimethanol dimethacrylate, trimethylolpropane trimethacrylate or mixtures thereof; iv) is a vinyl compound with a molecular weight of up to 10,000 g/mol; v) is selected from aliphatic and aromatic vinyl compounds; vi) is an allyl compound with a molecular weight of up to 10,000 g/mol; or vii) is selected from aliphatic and aromatic allyl compounds.

5. The photo-curable composition according to claim 1, wherein thiol groups:NCO groups: —C═C groups are present in an equivalent ratio of 0.7:0.05:1.3 to 1.3:1.3:0.05.

6. The photo-curable composition according to claim 1, wherein the at least one photolatent base catalyst i) is present in 0.01 to 5 wt.-%, based on the total weight of the composition; ii) is selected from 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate, 1,5,7-triazabicyclo[4.4.0]dec-5-ene hydrogen tetraphenyl borate, 2-benzyl-2-(dimethylamino)-1-(4-methoxyphenyl)butan-1-one, 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, 1-(anthracen-9-ylmethyl)-2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepin-1-ium tetraphenyl borate, 1-(anthracen-9-ylmethyl)-9-ethyl-3,4,6,7,8,9-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tetraphenyl borate, 2-benzyl-2-(dimethylamino)-1-(4-methoxyphenyl)butan-1-one, 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, 2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidin-1-ium tetraphenylborate, 1-(anthracen-9-ylmethyl)-2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidin-1-ium tetraphenylborate, 3-(anthracen-9-ylmethyl)-1-methyl-1H-imidazol-3-ium tetraphenylborate, 3,4,6,7,8,9-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tetraphenylborate, 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium n-butyltriphenylborate, (Z)-([Bis(dimethylamino)methylidene]amino)-N-cyclohexyl(cyclohexylamino)methaniminiumtetrakis(3-fluorophenyl)borate or mixtures thereof; or iii) releases a basic component, of which its protonated counterpart has a pKa of above 10.

7. The photo-curable composition according to claim 6, wherein the at least one additive i) is present in up to 10 wt.-%, based on the total weight of the composition; ii) comprises (E1) at least one inhibitor selected from acid boric esters or phosphoric acid esters; iii) comprises (E2) at least one compound selected from solvents, fillers, fire retardants, UV-stabilizer, pigments, dyes or mixtures thereof; iv) comprises (E3) at least one radical photoinitiator; or v) comprises (E4) at least one sensitizer.

8. The photo-curable composition according to claim 1, wherein the composition has a viscosity of 1 to 5,000 m*Pas measured with a AR2000 rheometer from TA instruments equipped with a Peltier plate and a 40 mm parallel plate at 25° C. in the shear stress range of 100 to 500 Pa.

9. A method of photo-curing the photo-curable composition according to claim 1, comprising of the steps: i) providing the photo-curable composition by i.a) mixing the components A) to D) and optionally E) or i.b) mixing A), D) and optionally E) and separately mixing B) and C) before mixing the mixture containing A), D) and optionally E) and the mixture containing B) and C); ii) transferring the photo-curable composition of step i) to a mould; iii) exposing the photo-curable composition to UV-light to obtain a cross-linked polymer; and iv) optionally post-curing the obtained polymer by thermal or UV treatment.

10. A method of three dimensional printing an object with the photo-curable composition according to claim 1, comprising of the steps: i) providing the photo-curable composition; ii) forming a layer of the photo-curable composition with a three dimensional printer; iii) exposing the layer under a suitable light source following a pattern of cross-sectional layer of the model to cure the layer; iv) providing a further layer of the photo-curable composition with the three dimensional printer upon the cured layer obtained after step iii); v) exposing the layer of step iv) under a suitable light source following a pattern of cross-sectional layer of the model in order to cure the layer and bond with the layer of step iii); and vi) optionally repeating steps iv) and v) until the three-dimensional object is obtained.

11. A cross-linked polymer obtained by the method according to claim 9.

12. A three-dimensional object obtained by the method according to claim 10.

13. The cross-linked polymer according to claim 11, having i) a glass transition temperature Tg of 0 to 200° C., measured according to ISO 11357-2:2014-07 or ASTM E1356-08(2014); and/or ii) a refractive index of 1.50 to 1.80, measured with an Electronic Abbe Refractometer AR 2008 from A.Krüss Optronic at 21° C. and at standard wavelength of 589 nm.

14. The three dimensional object according to claim 12 having i) a glass transition temperature Tg of 0 to 200° C., measured according to ISO 11357-2:2014-07 or ASTM E1356-08(2014); and/or ii) a refractive index of 1.50 to 1.80, measured with an Electronic Abbe Refractometer AR 2008 from A.Krüss Optronic at 21° C. and at standard wavelength of 589 nm.

Description

[0060] FIG. 1 is mentioned in [0062] and demonstrates the shape memory procedure as described in [0061].

[0061] FIG. 2 is mentioned in [0087] and shows a 3D SLA printed article.

EXAMPLES

[0062] Glass transition temperature:

The Tg of the samples was determined using a DSC Q2000 equipped with a Refrigerated Cooling System 90, both from TA instruments. The DSC experiments comprised two cooling/heating cycles at a scanning rate of 10° C./min using N.sub.2 as a purge gas. The measurement can be performed in accordance with ISO 11357-2:2014-07 or ASTM E1356-08(2014).

[0063] Refractive index (n.sub.D.sup.21):

The refractive index of the samples was measured using an Electronic Abbe Refractometer AR 2008 from A. Krüss Optronic. All measurements were performed at 21° C. and at standard wavelength of 589 nm.

[0064] Abbe's number (v.sub.D.sup.21)

The Abbe's number of the samples was measured using a Metricon 2010/M Prism Coupler equipped with three lamps emitting at 402, 511 and 687 nm. All measurements were performed at 21° C. and the value at A=589 nm was interpolated by the software.

[0065] Initial viscosity:

The initial viscosity of the formulations was measured using an AR2000 rheometer from TA instruments equipped with a Peltier plate and a 40 mm parallel plate. The viscosity of the formulations was checked at 25° C. in the shear stress range of 100-500 Pa.

[0066] Pot-life:

The pot-life of the formulations is defined as the time during which the viscosity remains below the viscosity limit of 3000 m*Pas. The pot-life was checked by monitoring the viscosity over time as above described.

[0067] Shape memory properties:

Shape memory properties of the samples were characterized using a manual procedure which consists of five steps:
1. Heat the sample at the programming temperature (T.sub.prog) which is above T.sub.trans.
2. Bend the sample at a specific angle and let it cool for 3 minutes while keeping the bent shape.
3. Remove the stress and measure the angle after one minute to see if it keeps the temporary shape (calculate R.sub.f).
4. Heat the sample for 1 minute at the recovery temperature (T.sub.rec) to allow the shape recovery.
5. Measure the angle after the recovery and calculate R.sub.r.

[0068] The shape recovery ratio (R.sub.r) and the shape fixity ratio (R.sub.f) are the two main parameters to asses the shape memory behavior. R.sub.f and R.sub.r represent the ability of the material to fix the temporary shape and the recovery to the original shape, respectively. These values are calculated using the following equations:

[00001]$R_f=\frac{{\epsilon }_u}{{\epsilon }_m}.Math.100;R_r=\frac{{\epsilon }_m-{\epsilon }_p}{{\epsilon }_m}.Math.100$

Where ε.sub.u is the temporary fixed strain (end of step 3), ε.sub.m is the applied strain (end of step 1) and ε.sub.p is the strain after the sample has recovered its original shape (end of step 4). Normally, the shape memory cycle is performed more than once to assess the consistency of R.sub.f and R.sub.r (FIG. 1).

Examples 1 and 2 and Comparative Example 1

[0069] The SH:NCO:methacrylate equivalent ratio was set at 1.1:0.8:0.2. 1.9085 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 1.7969 g of pentaerythritol tetra(3-mercaptopropionate) (Thiocure® PETMP) and 0.2946 g of trimethylolpropane trimethacrylate (SR351). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0040 g (0.05 wt.-%) of DBU-Ant-BPh4 were added to 1.7951 g of Thiocure® PETMP and mixed for 1 min at 3500 rpm. Afterwards, 1.9066 g of Desmodur® N3600 and 0.2943 g of SR351 were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 1). The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the acrylate peak (810/1630 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0070] The SH:NCO:methacrylate equivalent ratio was set at 1.1:0.8:0.2. 1.7812 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 1.6770 g of pentaerythritol tetra(3-mercaptopropionate) (Thiocure® PETMP) and 0.5419 g of isobornyl acrylate. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0040 g (0.1 wt.-%) of DBU-Ant-BPh4 were added to 1.6753 g of Thiocure® PETMP and mixed for 1 min at 3500 rpm. Afterwards, 1.7794 g of Desmodur® N3600 and 0.5413 g of isobornyl acrylate were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 2). The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the acrylate peak (810/1630 cm.sup.−1,) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0071] For comparison, a formulation with a SH:NCO:methacrylate equivalent ratio of 1.1:1.0:0.0 is prepared by adding 2.2793 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to 1.7167 g of pentaerythritol tetra(3-mercaptopropionate) (Thiocure® PETMP). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer.

[0072] A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0040 g (0.1 wt %) of DBU-Ant-BPh4 were added to 1.7167 g of Thiocure® PETMP and mixed for 1 min at 3500 rpm. Afterwards, 2.2793 g of Desmodur® N3600 were added to the previous mixture and were mixed for 1 min at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry (Comparative example 1).

TABLE-US-00001 SH:NCO:acrylate Initial Pot- T.sub.g Refractive Abbe's equivalent η life (° index number ratio (cP) (h) C.) (n.sub.D.sup.21) (v.sub.D.sup.21) Comparative 1.1:1:0 594 ~28 51 1.551 45.9 Ex. 1 Ex. 1 1.1:0.8:0.2 467 ~33 45 1.548 46.1 Ex. 2 1.1:0.8:0.2 292 ~50 38 1.566 47.7

[0073] Comparative example 1 is a binary formulation containing a multi-functional thiol and a multi-functional isocyanate which yields a viscous reactive formulation. On the other hand, Example 1 and Example 2 are ternary formulations containing three main components: a multi-functional thiol, a multi-functional isocyanate and a multi-functional ene monomer which in this case is a (meth)acrylate. These formulations are less viscous and, in some cases, are less reactive as seen by the extension of the pot-life. Regarding the optical properties, the refractive index can be boosted as seen with Example 2. The high Abbe's number values means a lower dispersion in the refractive index. The main improvements of Examples 1 and 2 are the reduction of the viscosity and the extension of the pot-life. Additionally, other desired properties such as the refractive index or the Abbe's number can be improved as well.

Examples 3 and 4 and Comparative Example 2

[0074] The SH:NCO:vinyl equivalent ratio was set at 1.1:0.75:0.25.1.9583 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 2.1285 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP) and 0.3463 g of 1,4-cyclohexane dimethanol divinyl ether. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst, and 2-hydroxy-2-methylpropiophenone (Darocur® 1173) as photoinitiator was UV cured. Firstly, 0.0022 g (0.05 wt.-%) of DBU-Ant-BPh4 and 0.0022 g (0.05 wt.-%) of Darocur® 1173 were added to 2.0811 g of Thiocure® Di-PETMP. The mixture was then speedmixed 1 min at 3500 rpm. Afterwards, 2.1817 g of Desmodur® N3600 and 0.3033 g of 1,4-cyclohexane dimethanol divinyl ether were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 3). The formulation was degassed under vacuum if there were bubbles present. Then the mixture was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the C—H out of the plane bending of the double bond peak (910 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0075] The SH:NCO:vinyl equivalent ratio was set at 1.1:0.5:0.5.1.3692 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 2.222 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP) and 0.7264 g of 1,4-cyclohexane dimethanol divinyl ether. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst and 2-hydroxy-2-methylpropiophenone (Darocur® 1173) as photoinitiator, was UV cured. Firstly, 0.0022 g (0.05 wt.-%) of DBU-Ant-BPh4 and 0.0022 g (0.05 wt.-%) of Darocur® 1173 were added to 2.0424 g of Thiocure® Di-PETMP. The mixture was then speedmixed 1 min at 3500 rpm. Afterwards, 1.3677 g of Desmodur® N3600 and 0.7256 g of 1,4-cyclohexane dimethanol divinyl ether were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 4). The formulation was degassed under vacuum if there were bubbles present. Then the mixture was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the C—H out of the plane bending of the double bond peak (910 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0076] For comparison, a formulation with a SH:NCO:vinyl equivalent ratio of 1.1:1.0:0.0 is prepared by adding 2.1901 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to 1.8079 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer.

[0077] A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0020 g (0.05 wt %) of DBU-Ant-BPh4 were added to 1.8079 g of Thiocure® DiPETMP and mixed for 1 min at 3500 rpm. Afterwards, 2.1901 g of Desmodur® N3600 were added to the previous mixture and were mixed for 1 min at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry (Comparative example 2).

TABLE-US-00002 SH:NCO:vinyl Initial Pot- T.sub.g Refractive equivalent η life (° index Storing ratio (cP) (h) C.) (n.sub.D.sup.21) conditions Comparative 1.1:1:0 1157 ~8 70 1.548 25° C. Ex. 2 Ex. 3 1.1:.75:0.25 744 ~24 52 1.556 25° C. Ex. 4 1.1:0.5:0.5 373 ~16 22 1.542 25° C.

[0078] Comparative Ex. 2 only contains a multi-functional thiol and a multi-functional isocyanate which yields a viscous reactive formulation. On the other hand, Examples 3 and 4 contain three main components: a multi-functional thiol, a multi-functional isocyanate and a multi-functional ene monomer which, in this case, are vinyls. These formulations are less viscous and, in some cases, are less reactive as seen by the extension of the pot-life. Thus, the main improvements of examples 3 and 4 are the reduction of the viscosity and the extension of the pot-life.

Example 5

[0079] The SH:NCO:vinyl equivalent ratio was set at 1.1:0.9:0.1.2.3782 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 2.2289 g of trimethylolpropane tris(3-mercaptobutyrate) (TMPTMB) and 0.0773 g of 1,2,4-trivinyl cyclohexane. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature (Comparative example 5). Two mixtures were prepared with the same composition: one was stored at 5° C. while the second was stored at room temperature (25° C.). The formulations viscosity was checked over time with a rheometer.

TABLE-US-00003 Storing SH:NCO:vinyl Initial η Pot-life conditions equivalent ratio (cP) (days) Example 5  5° C. 1.1:0.9:0.1 409 ~13 25° C. ~8

[0080] As seen in the table, by storing the formulations at low temperature (5° C.) the pot-life is extended from 8 days to 13 days. The extension is due to the fact that at low temperature the kinetics of the reaction in the dark are slowed down.

Examples 6 and 7 and Comparative Example 3

[0081] The SH:NCO:allyl equivalent ratio was set at 1.1:0.8:0.2. 2.0447 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 2.0835 g of Dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP) and 0.3402 g of diallyl phthalate. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer.

[0082] A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst and 2-hydroxy-2-methylpropiophenone (Darocur® 1173) as photoinitiator was UV cured. Firstly, 0.0022 g (0.05 wt.-%) of DBU-Ant-BPh4 and 0.0022 g (0.05 wt.-%) of Darocur® 1173 were added to 2.0811 g of Thiocure® Di-PETMP. The mixture was then speedmixed 1 min at 3500 rpm. Afterwards, 2.0424 g of Desmodur® N3600 and 0.3398 g of diallyl phthalate were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 6). The formulation was degassed under vacuum if there were bubbles present. Then the mixture was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the C—H out of the plane bending of the double bond peak (910 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0083] The SH:NCO:allyl equivalent ratio was set at 1.1:0.6:0.4. 1.5717 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 2.1354 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP) and 0.6974 g of diallyl phthalate. The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer. A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst and 2-hydroxy-2-methylpropiophenone (Darocur® 1173) as photoinitiator was UV cured. Firstly, 0.0022 g (0.05 wt.-%) of DBU-Ant-BPh4 and 0.0022 g (0.05 wt.-%) of Darocur® 1173 were added to 2.1331 g of Thiocure® Di-PETMP. The mixture was then speedmixed 1 min at 3500 rpm. Afterwards, 1.5700 g of Desmodur® N3600 and 0.6966 g of diallyl phthalate were added to the previous mixture and were mixed for 1 min at 3500 rpm (Example 7). The formulation was degassed under vacuum if there were bubbles present. Then the mixture was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the C—H out of the plane bending of the double bond peak (910 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry.

[0084] For comparison, a formulation with a SH:NCO:vinyl equivalent ratio of 1.1:1.0:0.0 is prepared by adding 2.1901 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to 1.8079 g of dipentaerythritol hexa(3-mercaptopropionate) (Thiocure® DiPETMP). The mixture was mixed for 1 min at 3500 rpm and stored at room temperature. The formulation viscosity was checked over time with a rheometer.

[0085] A formulation containing the same monomers but with a 1,8-diazabicyclo[5.4. 0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) as a photolatent base catalyst was UV cured. Firstly, 0.0020 g (0.05 wt.-%) of DBU-Ant-BPh4 were added to 1.8079 g of Thiocure® DiPETMP and mixed for 1 min at 3500 rpm. Afterwards, 2.1901 g of Desmodur® N3600 were added to the previous mixture and were mixed for 1 min at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The fully cured sample was characterized by DSC and refractometry (Comparative example 3).

TABLE-US-00004 SH:NCO:allyl Refractive equivalent Initial η Pot-life T.sub.g index ratio (cP) (h) (° C.) (n.sub.D.sup.21) Comparative 1.1:1:0 1157 ~8 70 1.548 Ex. 3 Ex. 6 1.1:0.8:0.2 705 ~16 53 1.565 Ex. 7 1.1:0.6:0.4 511 ~23 32 1.577

[0086] Comparative ex. 3 only contains a multi-functional thiol and a multi-functional isocyanate which yields a viscous reactive formulation. On the other hand, Example 6 and Example 7 contain three main components: a multi-functional thiol, a multi-functional isocyanate and a multi-functional ene monomer which, in this case, are allyls. These formulations are less viscous and, in some cases, are less reactive as seen by the extension of the pot-life. Thus, the main improvement of Examples 6 and 7 is the reduction of the viscosity and the extension of the pot-life. Also, it was observed that when adding an aromatic monomer (diallyl phthalate) the refractive index is boosted.

Examples 8 to 10 and Comparative Example 4

[0087] Samples containing Thiocure® PETMP, Desmodur® N3600 and 3-methylpentane-1,5-diyldiacrylate (SR341) with three different SH:NCO:acrylate equivalent ratios were prepared. As an illustrative example a formulation with a SH:NCO:acrylate equivalent ratio of 1.0:0.9:0.1 was prepared by adding 2.1842 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to a mixture of 1.6617 g of pentaerythritol tetra (3-mercaptopropionate) (Thiocure® PETMP) and 0.1501 g of 3-methylpentane-1,5-diyl diacrylate (SR341) (Example 8). The mixture is mixed for 1 minute at 3500 rpm. Then, 0.0040 g of 1,8-diazabicyclo[5.4.0]undec-7-ene-anthracene-tetraphenyl borate (DBU-Ant-BPh4) was added to make the formulation UV curable. After the addition of the catalyst the mixture is mixed for 1 minute at 3500 rpm. After mixing the formulation is degassed under vacuum, casted in the desired mould and placed in the UV curing chamber equipped with a Hg lamp. The mixture was irradiated 3 times for 10 seconds. The reaction conversion was monitored by the disappearance of the NCO peak (˜2260 cm.sup.−1) and the C—H out of the plane bending of the double bond peak (810 cm.sup.−1) by ATR-FTIR. If the reaction was not completed upon UV light exposure the sample was thermally post-cured. The formulations at other equivalent ratios were prepared following the same procedure but with the appropriate amounts (examples 9 and 10).

[0088] For comparison, a formulation with a SH:NCO:methacrylate equivalent ratio of 1.1:1.0:0.0 is prepared by adding 2.2793 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) to 1.7167 g of pentaerythritol tetra (3-mercaptopropionate) (Thiocure® PETMP). The mixture was mixed for 1 min at 3500 rpm. To this mixture, 0.0040 g of 1,8-diazabicyclo[5.4.0]undec-7-ene-Anthracene-Tetraphenyl borate (DBU-Ant-BPh4) are added and the mixture was mixed for 1 min at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present. Then the formulation was casted in the appropriate mould and placed in a UV curing chamber equipped with a Hg lamp. The formulation was irradiated 3 times for 10 seconds. If the reaction was not completed upon UV light exposure the sample was thermally post-cured (Comparative example 4).

[0089] The shape memory properties of the samples were measured by performing the shape memory test consisting of the following steps:

1. Heat the sample at the programming temperature (T.sub.prog) which is above T.sub.trans.
2. Bend the sample at 45° and let it cool for 3 minutes while keeping the bent shape.
3. Remove the stress and measure the angle after one minute to see if it keeps the temporary shape (calculate R.sub.f).
4. Heat the sample for 1 minute at the recovery temperature (T.sub.rec) to allow the shape recovery.
5. Wait 3 minutes to allow the sample to cool down, measure the angle after the recovery and calculate R.sub.r.

[0090] The strain (ε) at each step is calculated from the angles measured bearing in mind that a 100% deformation would be bending the sample 360°. Also, as some samples were not perfectly flat the initial angle (α.sub.o) is measured. The strain at each step is calculated using the following equations:

[00002]${\epsilon }_m=\frac{{\alpha }_0-{\alpha }_m}{360}.Math.100;{\epsilon }_u=\frac{{\alpha }_0-{\alpha }_u}{360}.Math.100;{\epsilon }_p=\frac{.Math.{\alpha }_0-{\alpha }_p.Math.}{360}.Math.100$

[0091] Where α.sub.o is the initial angle, am is the angle at which the sample is deformed, α.sub.u is the angle after the sample has fixed the temporary shape, α.sub.p is the angle after the shape recovery, ε.sub.m is the strain at which the sample is deformed, ε.sub.u is the strain after the sample has fixed the temporary shape and ε.sub.p is the strain after the shape recovery. The shape recovery ratio (R.sub.r) and the shape fixity ratio (R.sub.f) are the two main parameters to assess the shape memory behavior. R.sub.f and R.sub.r represent the ability of the material to fix the temporary shape and the ability to recover the original shape, respectively. The R.sub.r and R.sub.f are calculated using the following equations:

TABLE-US-00005 [00003]$R_f=\frac{{\epsilon }_u}{{\epsilon }_m}.Math.100;R_r=\frac{{\epsilon }_m-{\epsilon }_p}{{\epsilon }_m}.Math.100$ SH:NCO:acrylate ε.sub.m ε.sub.u ε.sub.p R.sub.f R.sub.r equivalent ratio α.sub.o (°) α.sub.m (°) (%) α.sub.u (°) (%) α.sub.p (°) (%) (%) (%) Comp. 1.0:1.0:0.0 170.1 135.0 9.8 148.8 5.9 171.6 0.4 60.7 95.7 Ex. 4 Ex. 8 1.0:0.9:0.1 177.0 135.0 11.7 135.0 11.7 176.5 0.1 100.0 98.8 Ex. 9 1.0:0.8:0.2 177.1 135.1 11.7 135.1 11.7 172.6 1.3 100.0 89.3 Ex. 10 1.0:0.7:0.3 177.5 135.1 11.8 136.2 11.5 172.2 1.5 97.4 87.5

[0092] As seen in the table, the addition of a third compound, in this case an aliphatic diacrylate, improves the shape memory properties. Specifically, there is a huge increase on the ability to fix the temporary shape from 60% (comparative example 4) to >97% for examples 8-10. As the acrylate ratio is increased, the recovery ratio decreases but it is still close to 90% which is ideal for shape memory applications.

Example 11

[0093] The SH:NCO:methacrylate equivalent ratio was set at 1.0:0.8:0.2. 39.9 g of tris(6-isocyanatohexyl)-1,3,5-triazinane-2,4,6-trione (Desmodur® N3600) are added to a mixture of 34.18 g of pentaerythritol tetra(3-mercaptopropionate) (Thiocure® PETMP) and 5.41 g ethylene glycol methacrylate (SR206). The mixture is mixed for 1 minute at 3500 rpm. To this mixture, 0.47 g (0.6 wt %) of 1-(anthracen-9-ylmethyl)-9-ethyl-3,4,6,7,8,9-hexahydro-2H-pyrimido[1,2-a]pyrimidin-1-ium tetraphenyl borate (EtGUA-Ant-BPh4) are added and mixed for 1 minute at 3500 rpm. The formulation was degassed under vacuum if there were bubbles present.

[0094] This formulation is used to prepare a 3D article using a SLA printer from Peopoly (Moai). The printer has a 405 nm wavelength light laser with a power of 150 mW. Printing was carried out with slice thickness of 0.1 mm. As an example, we printed a column shown in FIG. 2.